Microstructure and mechanical properties of a dilute Mg-Gd-Y-Zr alloy fabricated using wire-arc directed energy deposition additive manufacturing

Mg-Gd-Y-Zr is an important lightweight material in the aerospace field. However, the engineering applications of large-scale Mg-Gd-Y-Zr alloy components are significantly limited by macrosegregation and microstructure coarsening during the casting process. In recent years, wire-arc directed energy deposition (DED), which has high design and manufacturing freedom, provides a new route to manufacture large-scale metal parts. In this work, a dilute Mg-3.2Gd-0.6Y-0.5Zr (wt.%) alloy, which had a degree of alloying comparable to AZ31 commercial alloys, was fabricated using a wire-arc DED process based on tungsten inert gas (TIG) welding, the microstructure evolution, tensile properties, and impact toughness were investigated. Due to the multiple grain refinement effects, the DED sample displayed a fine-grain structure (12.3 +/- 7.4 mu m), which was comparable to that of the wrought counterpart. Combined with the ductilizing effects of the fine grain and the Gd/Y solutes, the DED sample achieved a high ductility, which was better than most reported additive-manufactured Mg alloys as well as wrought Mg alloys. The good plastic deformation capacity also endowed the DED sample with good crack propagation resistance under dynamic impact load. We hope this work can help guide the further development of high-performance Mg alloys that are specially designed for the wire-arc DED additive manufacturing process.